diff --git a/core/modules/system/lib/Drupal/system/Tests/Serialization/EntitySerializationTest.php b/core/modules/system/lib/Drupal/system/Tests/Serialization/EntitySerializationTest.php
index c866549..63e3da0 100644
--- a/core/modules/system/lib/Drupal/system/Tests/Serialization/EntitySerializationTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Serialization/EntitySerializationTest.php
@@ -121,15 +121,22 @@ public function testSerialize() {
     $expected = json_encode($normalized);
     // Test 'json'.
     $actual = $serializer->serialize($this->entity, 'json');
-    $this->assertIdentical($actual, $expected, 'Entity serializes to JSON when json is requested.');
+    $this->assertIdentical($actual, $expected, 'Entity serializes to JSON when "json" is requested.');
+    $actual = $serializer->serialize($normalized, 'json');
+    $this->assertIdentical($actual, $expected, 'A normalized array serializes to JSON when "json" is requested');
     // Test 'ajax'.
     $actual = $serializer->serialize($this->entity, 'ajax');
-    $this->assertIdentical($actual, $expected, 'Entity serializes to JSON when ajax is requested.');
+    $this->assertIdentical($actual, $expected, 'Entity serializes to JSON when "ajax" is requested.');
+    $actual = $serializer->serialize($normalized, 'ajax');
+    $this->assertIdentical($actual, $expected, 'A normalized array serializes to JSON when "ajax" is requested');
     // Test 'xml'. The expected output should match that of Symfony's XmlEncoder.
     $base_encoder = new BaseXmlEncoder();
+    $normalized = $serializer->normalize($this->entity, 'xml');
     // We need to pass the normalized array structure to this.
-    $expected = $base_encoder->encode($serializer->normalize($this->entity), 'xml');
+    $expected = $base_encoder->encode($normalized, 'xml');
     $actual = $serializer->serialize($this->entity, 'xml');
-    $this->assertIdentical($actual, $expected, 'Entity serializes to XML when xml is requested.');
+    $this->assertIdentical($actual, $expected, 'Entity serializes to XML when "xml" is requested.');
+    $actual = $serializer->serialize($normalized, 'xml');
+    $this->assertIdentical($actual, $expected, 'A normalized array serializes to XML when "xml" is requested');
   }
 }